1. Field of the Invention
The present invention relates to a digital signal reproducing apparatus for reproducing digital signals from a recording medium wherein each data block separately stores plural kinds of playback source signals in discrete areas thereof and, more particularly, to a digital signal reproducing apparatus for reproducing audio signals and video signals from compact disks to which are recorded still images using the CD-G (compact disk graphic) format, video CDs to which are recorded moving picture video sequences, and other types of similar digital disks.
2. Description of the Prior Art
A variety of standards have been established for the optical recording and reproducing medium such as a compact disk which is referred to as "CD" in recent years, and while the first CD players were audio-only reproducing devices, some types of CD players today can also reproduce motion video sequences with simultaneous audio accompaniment. One format and reproducing apparatus of this type is the CD-G (CD graphics) karaoke player for reproducing the still image data and the audio stored in the optical disks to displaying the lyrics and/or other still image on a television or other display device and to output the audio information through speakers.
In FIG. 11, a block diagram of an example of conventional digital reproducing apparatus for the playback of a CD-G disk or similar disk-shaped recording medium 1 is shown. A CD-graphic disk is an optically recorded digital disk to which is recorded both audio information and still image (graphic) information be reproduced, and is referred to as "disk" hereafter. According to the use's selection input to the apparatus, a controller 3 controls the operation thereof so that a signal reader 4 reproduces the digital data Sf stored in the specified area of the disk 1 to produce an audio information data Sa and a video information data Sr. The video information data Sr is also a sub-code signal containing the time code information and still image information.
A subcode extractor 6 extracts a subcode information Sc and a video information Sv from the data Sr which are transferred to a digital mute 17 and a video information mute 25, respectively. The digital mute 17 digitally mutes the digital audio data Sa and passes the muted data, or cancels muting and passes the non-muted data to a D/A converter 18 whereat those muted or non-muted digital audio data is converted to analog audio signal. An analog mute 19 mutes and passes the analog audio data from the D/A converter 18, or cancels muting and passes the non-muted signal to an amplifier 20 whereby the audio signal is amplified at a constant amplification factor. Thus power amplified audio signal is applied to a speaker 21 for converting to sound waves.
The video information mute 25 digitally mutes the digital video data Sv and passes the muted data, or cancels muting and passes the nun-muted data to an image data composer 26. The image data composer 26 composes and stores to a temporary video storage memory the image data required for video display based on the digital video data signal output from the video information mute 25. The image data generated by the image data composer 26 is displayed on a television or other video display means 28.
A reproduction position detector 7 detects the current reproduction position of the disk 1 from the sub-code information Sc. An access controller 5 drives the controller 3 to access the desired reproduction position of the disk 1. An address storage 8 stores the disk address output from the reproduction position detector 7 when access by the access controller 5 is completed. When access by the access controller 5 is completed, the analog muting canceler 16 cancels the muting applied by the analog mute 19. The address comparator 10 compares the value of the output from the address storage 8 with that from the reproduction position detector 7 to produce an address comparison signal Sp.
When access by the access controller 5 is completed, the pause controller 9 pauses at that address for a predetermined period based on the address comparison signal Sp. When the predetermined pause imposed by the pause controller 9 is completed, the re-access controller 11 re-accesses the reproduction position of the disk 1 stored in the address storage 8. A reproducer 29 produces a reproduction command signal Sd so as to begin reproducing the disk when the access operation executed by the re-access controller 11 is confirmed completed based on the output from the address comparator 10.
After re-access is completed and it is confirmed based on the output of the address comparator 10 that the reproducer 29 has passed the reproduction position stored in the address storage 8, a digital muting canceler 15 produces a digital muting cancelling signal Sac to cancel muting by the digital mute 17. After the transition to the reproduction operation of the reproducer 29 is completed, and the reproduction position stored in the address storage 8 is detected to have been passed based on the output from the address comparator 10, a video muting canceler 24 produces video mute canceling signal Svc to cancel muting by a video information mute 25.
Note that the components contained within the dotted line in FIG. 11 are typically comprised within a microcomputer 27, which with the appropriate software achieves and controls the major functions of the digital signal reproducing apparatus.
The specific operation of this conventional digital signal reproducing apparatus of FIG. 11 when reproducing a CD-G type disk is described below with reference to FIGS. 12 and 13. In FIG. 12, a flow chart of the major parts of the process executed by the microcomputer 27 is shown.
At step S101 in FIG. 12, when a START reproduction switch (not shown in the figures) of the keyboard 2 becomes ON, the control advances to step S102. At step S102, the access operation for accessing the disk selection specified by the user for reproduction is started, and the signal reader 4 drives the disk 1 to read the selected information therefrom.
It is then determined at step S103 whether access is completed or not. This is accomplished by the subcode extractor 6 extracting the subcode information in the data read from the disk 1 by the signal reader 4, and confirming the reproduction position of the disk 1 based on information input to the microcomputer 27. More specifically, this conventional digital signal reproducing apparatus does not consider access to be completed when the optical pickup is located at any disk address other than that of the specified selection; access is completed when the optical pickup enters the specified selection after tracking the pit stream recorded to the disk 1.
Note that the address is not accessed by accessing the end of the selection preceding the desired selection, and then tracking forward from there as during normal reproduction. When access is not completed, step S103 loops back to step S102, jumps the pickup several tracks forward and back of the current position, and then re-evaluates whether access is completed. This loop of steps S102 and S103 is repeated until access is completed.
It is assumed below that after accessing the end of the track preceding the desired track, the pit path of the disk 1 is followed until the desired track is entered, and it is determined based on the subcode information that the desired track has been accessed.
At step S104, the subcode information from the disk 1 is stored to the microcomputer 27 as the accessed address information. It is to be noted that a CD-G disk wherein the video data DV and audio data DA are arranged, as shown in FIG. 13, is used as the disk 1 in this example.
If the user selects TNO=2, i.e., the second selection, blocks A to D in FIG. 13 are reproduced from TNO=1, and blocks E to I are reproduced from TNO=2. If access is completed, the signal reader 4 has sequentially reproduced blocks A to D of the information recorded to the disk 1, and it is detected that the signal reader 4 has begun reproducing block E. At this time the address on the disk 1 is assumed to be 5M00S00F meaning of 5 minutes 0 seconds 0 frames.
It is further assumed that the audio signal and the CD-G video signal start simultaneously from this block E. In actuality, however, the microcomputer 27 is unable to determine at the point the signal reader 4 begins to read the location of 5M00S00F on the disk 1 that access is completed. This determination is delayed by the time required for the signal reader 4 to read the data from the disk 1, the time required for the microcomputer 27 to read the subcode information extracted by the subcode extractor 6, and the time required for the evaluation itself. However, the microcomputer 27 therefore also reads the address information when the subcode information for the desired track (TNO=2) matches the address information at 5M00S00F, and the microcomputer 27 therefore stores in step S104 the disk address of 5M00S00F as the address at which access was completed.
The muting applied by the analog mute 19 is cancelled in step S105. This is because the response time of the analog mute 19, which precedes the amplifier 20 outputting to the speaker 21, is typically slow, and may be as long as approximately 100 msec. depending upon the integrated circuits and other components used as the speaker 21. In this example, analog muting is cancelled at the point access is completed, a pause state is then entered and held for a predetermined period (500 msec. in this example) until muting by the analog mute 19 is completely cancelled, the disk is then re-accessed, and the analog audio signal from the D/A converter 18 is input to the analog mute 19.
It is to be noted that the signal reader 4 is paused in step S106 to wait for muting by the analog mute 19 to be completely cancelled. Once the pause is initiated, the predetermined pause period is then counted in step S107. In addition, the signal reader 4 is paused at the 5M00S00F address of the disk 1 while the loop of steps 106 and 107 is executed, i.e., until the 500-msec. pause period of this example is completed.
Note, further, that the pause operation of this example refers to an operating loop whereby tracking is adjusted when the signal reader 4 exceeds the 5M00S00F address to move to a point before the 5M00S00F address, and the subcode information is read again to reposition the signal reader 4 as necessary. After the 500 msec. pause period is completed, the re-access operation is executed at step S108.
This re-access operation differs from the access operation executed in step S102, and seeks the disk position of the 5M00S00F address at which access was previously completed. This operation can be completed more quickly and easily than can re-executing the access operation of step S102.
It is then determined in step S109 whether re-access is completed. More specifically, access is completed when the optical pickup reaches the location of 5M00S00F on disk 1 after tracking the pit stream recorded to the disk 1; re-access is not executed by seeking an address before 5M00S00F and then tracking normally forward from there to 5M00S00F. If re-access is not completed, step S109 loops back to step S108, jumps the pickup several tracks forward and reverse of the current position, and then re-evaluates whether access is completed.
When re-access is completed, video muting is cancelled at step S110 so that the video information from the signal reader 4, and the subcode extractor 6 can be passed to the image data composer 26. The digital mute 17 is then controlled at step S111 to cancel digital muting and throughput the audio information from the signal reader 4 to the D/A converter 18.
In FIG. 13, a timing chart used to describe the operation for reading information recorded to the disk 1 by the conventional digital signal reproducing apparatus of FIG. 11 is shown. Note that an arrow Sm schematically represents the movement of the pickup of signal reader 4 with respect to the formatted recording data Sf stored in the disk 1.
The data Sf includes data blocks A to I and the followings sequentially arranged. Each data block further includes an audio data DA and a video data DV. The data track is changed from track TNO=1 to TNO=2 in block E wherein the video data DA includes image clear command CC therein. and a line St represents the track number which the microcomputer 27 detects. Also state of signals Sp, Sd, Svc, Sac, Svr, and Sar observed in the convention digital signal reproducing apparatus are shown.
With a conventional digital signal reproducing apparatus as thus described, the audio and video information recorded to the disk 1 and selected by the user is output by means of speaker 21 and video display 28.
However, with a conventional digital signal reproducing apparatus as described above, the first part of the video and audio information recorded to the disk 1 and selected by the user will be dropped and not output from the speaker 21 and video display 28 if the video information and audio information recorded to the disk start simultaneously from the first block of the user selection, as shown in FIG. 13. This is described below with reference to FIG. 13.
The completion of disk access detected in step S109 in FIG. 12 is confirmed after reproduction of the block E containing the 5M00S00F address subcode read by the microcomputer.27 from the output of the subcode extractor 6 is completed.
Even if access is confirmed completed at the beginning of block F by the microcomputer 27, and cancellation of video information muting and digital muting in steps S110 and S111 is delayed only one frame due to the processing time constraints of the program output from the microcomputer 27, the actual cancellation of this muting will not occur until the beginning of block G, as shown in FIG. 13. In addition, processing of the video and audio information by the D/A converter 18 and image data composer 26 does not begin immediately upon muting cancellation because there is normally a time delay caused by serial transmission of the muting cancellation signal, and because a certain amount of time is required after transmission of the muting cancellation signal to the digital mute 17 and video information mute 25 before video and audio information processing by the D/A converter 18 and image data composer 26 can begin.
As a result, processing of the video information by the image data composer 26 is delayed two frames after video muting is cancelled and starts at as indicating of block I, as indicated by signal Svr; and processing of the audio information by the D/A converter 18 is delayed one frame after digital muting is cancelled and starts at the beginning of block H as indicated by signal Sar. As a result, both video and audio information are dropped during blocks E-G.
While the first part of the audio information is thus dropped and abnormal sounds may result, the loss of video information in the CD-G format is even more severe: when a "clear screen" command (a "PRESET MEMORY" command) in block. E is included, and the user selects TNO=2 while a selection other than TNO=2 is being reproduced from a CD-G formatted disk, the video portion of that non-TNO=2 selection currently displayed on the video display 28 will not be cleared, the video portion of TNO=2 will be superimposed to the video already displayed, and it will not be possible to satisfactorily view either video portion.